LambdaCDM Fails Again

LambdaCDM fails again

LambdaCDM again fails to reproduce what we observe. The latest paper below provides yet another independent case of that, based upon large scale clustering in certain kinds of dwarf galaxies, to add to the dozens of independent conflicts between LambdaCDM already identified. See, e.g., this January 25, 2021 post and this March 2, 2023 post.

The galaxy correlation function serves as a fundamental tool for studying cosmology, galaxy formation, and the nature of dark matter. It is well established that more massive, redder and more compact galaxies tend to have stronger clustering in space. These results can be understood in terms of galaxy formation in Cold Dark Matter (CDM) halos of different mass and assembly history. 

Here, we report an unexpectedly strong large-scale clustering for isolated, diffuse and blue dwarf galaxies, comparable to that seen for massive galaxy groups but much stronger than that expected from their halo mass. Our analysis indicates that the strong clustering aligns with the halo assembly bias seen in simulations with the standard ΛCDM cosmology only if more diffuse dwarfs formed in low-mass halos of older ages. This pattern is not reproduced by existing models of galaxy evolution in a ΛCDM framework, and our finding provides new clues for the search of more viable models. 

Our results can be explained well by assuming self-interacting dark matter, suggesting that such a scenario should be considered seriously.

Ziwen Zhang, et al., "Unexpected clustering pattern in dwarf galaxies challenges formation models" arXiv:2504.03305 (April 7, 2025) (Accepted for publication in Nature).

SIDM models don't solve the problem

This paper suggests that self-interacting dark matter could solve this particular problem, although the cross-section of interaction parameter preferred by this paper of 3.0 cm^2/g has already been ruled out in multiple prior studies, which constrain that cross-section of interaction to be 0.2 cm^2/g or less. 

Numerous prior papers, likewise demonstrate that SIDM has multiple serious problems of its own. See, e.g., posts on March 19, 2025 (cross-section of interaction must be under 0.2), July 25, 2023 (outliers, be they large cores or cuspy systems, are not readily accounted for), December 1, 2022 (strong correlation between visible matter and dark matter phenomena is a problem), February 2, 2022 (cross-section needs to be 0.5-1.0), August 11, 2020 (strong correlation between visible matter and dark matter phenomena is a problem), February 20, 2020 (SIDM shares the impossible early galaxies problem with LambdaCDM), November 23, 2018 (SIDM's multiple parameters fail Occam's Razor), October 23, 2017 (strong correlation between visible matter and dark matter phenomena is a problem), July 5, 2017 (strong correlation between visible matter and dark matter phenomena is a problem), December 6, 2016 (lack of DM annihilation signals rules out most SIDM models), and December 20, 2015 (cross-section should exceed 2.0 of the differences from LambdaCDM are too small). 

The literature on SIDM is obviously larger than what I discuss in these eleven posts (some of which identify the same problems or reference the same source papers). But I haven't posted too much about SIDM theories (there are 221 arXiv preprints that use the term, one of which appeared just today), in part, because they aren't very promising. Some of them, however, like a January 11, 2024 paper, and a July 12, 2023 paper place strict additional observationally derived constraints on the allowed parameter space of SIDM theories.

In general, the observational astronomy data places mutually inconsistent constraints on the cross-section of interaction in SIDM theories, can't explain the tight correlation of dark matter phenomena with visible matter distributions, can't explain outlier galaxies, doesn't produce expected dark matter annihilations, and shares the impossible early galaxies problem with cold dark matter theories.

Almost all dark matter particle theories are ruled out

In short, ΛCDM doesn't work, and SIDM doesn't work either. 

As previous posts at this blog have demonstrated based upon other papers, warm dark matter doesn't work. Primordial black holes don't work. MACHOs don't work. WIMPS don't work. And, strong force bound dark matter particles don't work.

Axion-like bosonic dark matter particles (ALP theories) with extremely small masses (comparable to the mass-energy of gravitons) aren't entirely ruled out yet, but are quite tightly constrained themselves. But this is pretty much the only remaining class of dark matter particle theories that aren't excluded.

Some gravity based explanations don't work

There are also some gravity based approaches that don't work. Ordinary gravitomagnetic effects don't get the job done, for example. And, we know that simple toy-model MOND itself is not an accurate description of reality either, even though it works and is predictive over a domain of applicability that covers almost all non-relativistic systems of galaxy size or smaller (although the wide-binary star case remains an open question and there may be problems with it far from the main plane of spiral galaxies).

But gravity based approaches (and there are far more of them out there than most people realize), at least, address one of the big problems that is generic in any dark matter particle theory, which is that dark matter phenomena are very tightly correlated with the distribution of ordinary matter in a gravitationally bound system.

Any gravity based approach which reproduced MOND effects over the entire range of single galaxies, moreover, is a good share of the way to being right. A good model, however, must, at least, also do better at being consistent with galaxy cluster phenomena. 

Conclusion: Lots of leading explanations are ruled out

In conclusion, the already established observational constraints, taken together, dramatically reduces the universe of explanations for dark matter phenomena that work, and in particular, eliminates many of the most heavily researched and mainstream explanations for it.